英文:
Firebase Retrieve Data Failed
问题
我遇到了这个错误：
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.posinventory/com.example.posinventory.Bill}: java.lang.NullPointerException: Attempt to invoke virtual method 'com.google.firebase.database.DatabaseReference com.google.firebase.database.FirebaseDatabase.getReference(java.lang.String)' on a null object reference
我发现当我尝试将以下代码添加到我的代码中时出现了这个错误：
di = mDatabase.getReference("transaction").child("Bill").child(id);
这是从Transaction子节点Bill数据库获取数据的整个代码：
public class Bill extends AppCompatActivity {
// ... （这里省略了一部分变量声明）
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// ... （这里省略了一部分界面初始化的代码）
// 初始化 Firebase 数据库
mDatabase = FirebaseDatabase.getInstance();
// ... （这里省略了一部分界面元素的初始化代码）
// 获取 info 数据
du = mDatabase.getReference("info");
du.keepSynced(true);
du.addListenerForSingleValueEvent(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
// ... （这里省略了一部分处理 info 数据的代码）
}
@Override
public void onCancelled(DatabaseError error) {
}
});
Intent intent = getIntent();
String id = intent.getStringExtra("key");
// 获取 transaction 数据
di = mDatabase.getReference("transaction").child("Bill").child(id);
di.keepSynced(true);
di.addListenerForSingleValueEvent(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
// ... （这里省略了一部分处理 transaction 数据的代码）
}
@Override
public void onCancelled(DatabaseError error) {
}
});
}
}
Firebase 数据库截图：
英文:
I get this error:
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.posinventory/com.example.posinventory.Bill}: java.lang.NullPointerException: Attempt to invoke virtual method 'com.google.firebase.database.DatabaseReference com.google.firebase.database.FirebaseDatabase.getReference(java.lang.String)' on a null object reference
and I found out that when I try to add di = mDatabase.getReference("transaction").child("Bill").child(id); into my code.
This is the whole code to get data from Transaction child Bill database
public class Bill extends AppCompatActivity {
TextView ph1, ph2, storename, storeaddr, transid, dlnum, date, gst, ptname, age, docname, totamt, name;
TextView medname[], unit[], batch[], qty[], rate[], exp[], amt[];
String ids[];
private DatabaseReference du;
private DatabaseReference di;
private FirebaseDatabase mDatabase;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
requestWindowFeature(Window.FEATURE_NO_TITLE);
this.getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN,
WindowManager.LayoutParams.FLAG_FULLSCREEN);
setContentView(R.layout.invoice);
getSupportActionBar().hide();
ph1 = (TextView) findViewById(R.id.ph1);
ph2 = (TextView) findViewById(R.id.ph2);
storename = (TextView) findViewById(R.id.storename);
storeaddr = (TextView) findViewById(R.id.storeaddr);
transid = (TextView) findViewById(R.id.transid);
dlnum = (TextView) findViewById(R.id.dlnum);
date = (TextView) findViewById(R.id.date);
gst = (TextView) findViewById(R.id.gst);
ptname = (TextView) findViewById(R.id.ptname);
age = (TextView) findViewById(R.id.age);
docname = (TextView) findViewById(R.id.docname);
totamt = (TextView) findViewById(R.id.totamt);
name = (TextView) findViewById(R.id.name);
medname = new TextView[4];
qty = new TextView[4];
amt = new TextView[4];
ids = new String[] { "medname", "qty", "amt" };
for (int j = 1; j <= 4; j++) {
medname[j - 1] = (TextView) findViewById(getResources().getIdentifier(ids[0] + j, "id", getPackageName()));
qty[j - 1] = (TextView) findViewById(getResources().getIdentifier(ids[1] + j, "id", getPackageName()));
amt[j - 1] = (TextView) findViewById(getResources().getIdentifier(ids[2] + j, "id", getPackageName()));
}
du = mDatabase.getReference("info");
du.keepSynced(true);
du.addListenerForSingleValueEvent(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
GenericTypeIndicator<Map<String, String>> genericTypeIndicator = new GenericTypeIndicator<Map<String, String>>() {
};
Map<String, String> map = dataSnapshot.getValue(genericTypeIndicator);
name.setText(map.get("name"));
storename.setText(map.get("storename"));
dlnum.setText(map.get("tin"));
storeaddr.setText(map.get("addr"));
ph1.setText("Ph: " + map.get("ph1"));
ph2.setText("Ph: " + map.get("ph2"));
gst.setText(map.get("gst"));
}
@Override
public void onCancelled(DatabaseError error) {
}
});
Intent intent = getIntent();
String id = intent.getStringExtra("key");
di = mDatabase.getReference("transaction").child("Bill").child(id);
di.keepSynced(true);
di.addListenerForSingleValueEvent(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
GenericTypeIndicator<Map<String, String>> genericTypeIndicator = new GenericTypeIndicator<Map<String, String>>() {
};
Map<String, String> map = dataSnapshot.getValue(genericTypeIndicator);
totamt.setText(map.get("gtotamt"));
date.setText(map.get("gdate"));
String items = map.get("gitems");
StringTokenizer st = new StringTokenizer(items, "®");
int k = -1;
while (st.hasMoreTokens()) {
k++;
// Toast.makeText(Bill.this,""+k , Toast.LENGTH_SHORT).show();
StringTokenizer sti = new StringTokenizer(st.nextToken(), "©");
while (sti.hasMoreTokens()) {
medname[k].setText(sti.nextToken());
qty[k].setText(sti.nextToken());
amt[k].setText(sti.nextToken());
}
}
}
@Override
public void onCancelled(DatabaseError error) {
}
});
}
}
Firebase Database:
答案1
得分: 0
你尚未声明getInstance()。尝试添加以下内容：
du = mDatabase.getInstance().getReference("info")
以及
di = mDatabase.getInstance().getReference("transaction").child("Bill").child(id)
我的意思是，当你遇到mDatabase时，在其后面加上getInstance()。然后告诉我更新情况。
英文:
you have not declared getInstance(). Try adding
du = mDatabase.getInstance().getReference("info") and
di =mDatabase.getInstance().getReference("transaction").child("Bill").child(id)
. I mean when you face a mDatabase add a getInstance() to it. And let me know the update.
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